Reforming our nation's educational system has created the need for new ways to assess the students' performance. The trend among educators, parents, and politicians to accommodate diversity in the student body demands new systems that accurately gauge the progress of students in relation to their peers while allowing for differences in what students know and how they acquire knowledge. This collection of essays addresses the problems - technical, political, and intellectual - of designing such a system. The first section discusses the concepts of learning that underpin different approaches to performance assessment. These essays compare notions of fixed intelligence and developmental learning and outline the need to acknowledge and support diversity in America's classrooms. The second section considers the political issues surrounding assessment systems that have been pilot-tested in Connecticut, Vermont, and Kentucky. The third and final section reviews design possibilities for future systems to assess both aptitude and achievement.